Moderate -0.8 This is a straightforward application of the binomial expansion formula for fractional powers with n=1/2, requiring only substitution and simplification to find four terms, plus stating the standard validity condition |2x|<1. It's more routine than average, involving direct recall of a standard technique with minimal problem-solving.
Find the first four terms in the binomial expansion of $\sqrt{1+2x}$. State the set of values of $x$ for which the expansion is valid. [5]
\hfill \mbox{\textit{OCR MEI C4 2012 Q2 [5]}}